Listeriosis
One Tough Bug HYG-5562-98 Nancy Stehulak
Listeria are bacteria found frequently in the environment. One listeria species, Listeria monocytogenes, can cause the serious foodborne illness "listeriosis." Listeriosis is a bacterial infection. Approximately 425 deaths occur each year in the United States due to L. monocytogenes.
L. monocytogenes is somewhat unusual in that it will grow at refrigeration temperatures. It is slightly more heat resistant than many other bacteria such as salmonella and E. coli, and will grow at temperatures as high as 140 to 150 degrees F. It will not survive pasteurization or heat treatment. Freezing seems to have little effect on the bacteria.
Where does L. monocytogenes come from? L. monocytogenes has been found in soil, leaf litter, sewage, silage, dust, and water. The organism often moves through animals and humans without causing illness, and has been found in many domestic and wild animals, including birds and fish.
It has only been in the last decade that L. monocytogenes has been recognized as an agent of foodborne illness.
Who is at risk? Healthy people rarely contract listeriosis, but the illness can be serious for some people, especially the elderly, newborns, pregnant women, and those with weakened immune systems.
Foods Associated with Listeriosis L. monocytogenes has been associated with such foods as raw milk, unpasteurized milk, cheeses (particularly soft-ripened varieties), ice cream, raw vegetables, raw-meat sausages, raw and cooked poultry, raw meats (all types), and raw and smoked fish. Its ability to grow at temperatures as low as 37 degrees F permits multiplication in refrigerated foods.
The Illness-What are the symptoms? Consumers most commonly contract listeriosis by eating food contaminated with the organism. Healthy people do not often develop noticeable listeriosis symptoms after eating food containing L. monocytogenes. The highest incidence of listeriosis has been in persons over 60 years old and newborns. Infections that occur during pregnancy may lead to miscarriages or serious illness in newborns. Others most at risk include those with compromised immune systems due to cancer, AIDS, or medications that impact the immune system.
Symptoms are fever, fatigue, nausea, vomiting, and diarrhea. More serious symptoms can result in meningitis (brain infections) and septicemia (bacteria in the bloodstream). Pregnant women may contract flu-like symptoms of listeriosis; complications can result in miscarriage, stillbirth, or meningitis in the newborn.
How can I reduce my risk? L. monocytogenes in food cannot be seen, tasted, or smelled. Common sense and simple precautions that apply to any foodborne illness should be used. Good sanitation, personal hygiene, and safe buying, storing, cooking, and serving methods, when applied in home, retail, and food service environments, can reduce the risk of problems with L. monocytogenes.
Although most of the population is at very low risk for listeriosis, the risk can be reduced if you:
1. Thoroughly cook all food of animal origin.
2. Wash raw vegetables thoroughly before eating.
3. Keep uncooked meats separate from vegetables, cooked foods, and ready-to-eat foods.
4. Avoid raw/unpasteurized milk or foods made from raw milk.
5. Wash hands, knives, and cutting boards after handling uncooked foods.
6. Read and follow label instructions to "keep refrigerated" and "use by" a certain date.
References 1. U.S. Department of Agriculture, Food Safety and Inspection Service, Background Document March 1992. Preventing Foodborne Listeriosis.
For more information on foodborne illness, contact your local county Extension Agent. See also the additional fact sheets on foodborne illness.
A Case in Point ... In 1985, an outbreak of Listeriosis, due to Mexican-style cheese, led to 18 deaths and numerous stillbirths. As a result of this episode, FDA has been monitoring domestic and imported cheeses and has taken numerous actions to remove these products from the market when L. monocytogenes is found.
The Center for Disease Control has established an epidemiological link between consumption of raw hot dogs or under cooked chicken in approximately 20% of the sporadic cases under study.
Source: U.S. Department of Agriculture, Food and Safety Inspection Service, Food and Drug Administration, Background Document, March, April 1992.
This material is based on work supported by the Extension Service, U.S. Department of Agriculture, under special project number 96-EFSF-0-3500.
How does Listeria monocytogenes get into food?
Animals can carry Listeria monocytogenes in their intestines without becoming sick. As a result, the bacteria may be spread to meat and dairy products. Listeria monocytogenes is killed by cooking or by other heating methods, such as pasteurization, used to produce ready-to-eat foods. However, ready-to-eat food can become contaminated after processing within the processing plant or along the route from the plant to your plate. Outbreaks of listeriosis are associated with ready-to-eat foods such as hot dogs, luncheon meats, cold cuts, fermented or dry sausage, and other deli-style meat and poultry. In the home, Listeria monocytogenes is destroyed if ready-to-eat foods are reheated to steaming hot
How does Listeria get into food? Listeria monocytogenes is found in soil and water. Vegetables can become contaminated from the soil or from manure used as fertilizer. Animals can carry the bacterium without appearing ill and can contaminate foods of animal origin such as meats and dairy products. The bacterium has been found in a variety of raw foods, such as uncooked meats and vegetables, as well as in processed foods that become contaminated after processing, such as soft cheeses and cold cuts at the deli counter. Unpasteurized (raw) milk or foods made from unpasteurized milk may contain the bacterium.
Listeria is killed by pasteurization and cooking; however, in certain ready-to-eat foods such as hot dogs and deli meats, contamination may occur after cooking but before packaging.
And the Food and Drug Administration is currently doing an investigation at the farm to figure out why, so we can prevent future cases of contamination. But the skin, the flesh of the cantaloupe is actually a good place for bacteria to grow. Listeria is quite unusual as a bacteria for a couple of reasons.
One is that, once you eat it, it may be one to three weeks or even one or two months before you become ill. And that's the main reason we expect to see, unfortunately, case numbers rising in the coming weeks. And the second is that it's one of those rare bacteria that can actually grow even when it's refrigerated.
So as you put it in your refrigerator, most food, even if it's contaminated, you will knock down that contamination. But with listeria, the bacteria can continue to grow in your refrigerator, and that's why we tell people to throw out anything from Jensen Farms, any cantaloupe from Jensen Farms.
What's tricky about listeria is that unlike most food-borne pathogens, it can multiply in the refrigerator. Pasteurization and cooking will kill the listeria bacterium, but contamination often occurs later in processing. So you might bring home some ready-to-eat deli meats, hot dogs or soft cheeses that have a trace of listeria contamination on them, put them in the fridge and a week or so later, while they still look fresh, find yourself eating a listeria-packed meal. Not that you would know right away. The symptoms of listeriosis can take anywhere from a few days to a few weeks to show up.
A nationwide listeria outbreak that as killed 25 people who ate tainted cantaloupe was probably caused by unsanitary conditions in the packing shed of the Colorado farm where the melons were grown, federal officials said Wednesday.
Government investigators said that workers had tramped through pools of water where listeria was likely to grow, tracking the deadly bacteria around the shed, which was operated by Jensen Farms, in Granada, Colo. The pathogen was found on a conveyor belt for carrying cantaloupes, a melon drying area and a floor drain, among other places.
“You’re rolling around cantaloupe on uncleanable equipment and you’re getting it wet and you’re not cooling it — it provides the perfect environment for listeria growth and spread,” said James Gorny, a senior food safety adviser at the Food and Drug Administration.
The outbreak, which began in late July, is the deadliest caused by foodborne disease since 1985. A total of 123 people in 26 states have fallen ill, including those who died, according to the Centers for Disease Control and Prevention.
Nicholas J. Parolisi Jr., a lawyer for Jensen Farms, said he could not comment on the F.D.A.’s accusations.
The farm had passed a food safety audit by an outside contractor just days before the outbreak began. Eric Jensen, a member of the family that runs the farm, said in an e-mail that the auditor had given the packing plant a score of 96 points out of 100.
F.D.A. officials did not criticize the auditor directly. But Michael R. Taylor, deputy commissioner for foods, said the agency intended to establish standards for how auditors should be trained and how audits should be conducted.
The food industry increasingly has come to rely on what it calls third-party audits of farms or processing plants to ensure the safety of food. But the auditors are hired by the companies being inspected, and their procedures are largely unregulated. In several recent food safety lapses, the facilities involved had passed third-party audits.
It was not clear how listeria initially got into the packing shed, which officials described as an open-air structure having a concrete floor, a roof and no walls.
Listeria is frequently found in soil or manure, but tests of the soil on the farm did not turn up the bacteria. Officials said that a dump truck used to take culled melons to a cattle farm was parked near the processing shed and could have brought bacteria to the facility.
Jensen Farms, run by Mr. Jensen and his brother Ryan, had recently acquired a set of used machinery to upgrade the way it washed and dried its cantaloupes. The equipment had been used to clean potatoes and was not intended for use with cantaloupes, officials said. They said the equipment was corroded in places and built in a way that made it difficult to clean and sanitize.
An area used to dry the melons included a cloth cover that could easily have harbored the bacteria, according to a person who discussed the operation with the Jensens.
Officials also said that the cantaloupes had not been adequately cooled before they were placed in refrigerated storage, which could have caused condensation to form on the fruit, creating hospitable conditions for listeria. The bacteria grow well in wet or damp conditions and can also thrive in cold.
Dr. Gorny said that some of the conditions he described, including pools of water on the floor, had been noted during a visit in mid-September after the plant ceased operation and the equipment was dismantled. It was not clear if investigators who had visited the plant while it was still in operation saw the same unsanitary conditions.
Officials said that conditions at Jensen Farms were not typical of the produce industry.
“We have no reason to believe these factors are indicative of practices throughout the industry,” said Sherri McGarry, a senior F.D.A. adviser.
The outbreak is likely to focus new attention on the use of auditors in the food industry. Typically farms or processors are required by their customers, like supermarket or restaurant chains, to have an auditor evaluate their food safety procedures.
Jensen Farms hired an auditor called PrimusLabs, based in California, to inspect its facility. Primus gave the job to a subcontractor, Bio Food Safety, which is based in Texas. Jensen and Primus declined to provide a copy of the audit report.
Robert Stovicek, the president of PrimusLabs, said his company had reviewed the audit and found no problems in how it was conducted or in the auditor’s conclusions.
“We thought he did a pretty good job,” Mr. Stovicek said. He said the auditor, James M. DiIorio, has been doing audits for the company since March.
He said that Mr. DiIorio had received two one-week training courses as part of his preparation and had also gone on audits with other auditors.
Asked how Mr. DiIorio could have given high marks to a facility that the F.D.A. described as a breeding ground for listeria, Mr. Stovicek said, “There’s lots of variations as to how people interpret unsanitary conditions.”
Mr. DiIorio did not return phone calls seeking comment.
Trevor V. Suslow, a professor of food safety at the University of California, Davis, said auditors may give farmers, processors and retailers a false sense of security. “There needs to be training, certification and auditing of the auditors,” he said.
Listeria can cause high fever and diarrhea, and cases can be especially severe among older people or those with weakened immune systems. Most of the people who died in the outbreak and many others who fell ill were elderly.
Herbert H. Stevens Jr., 84, of Littleton, Colo., became ill with a high fever on Aug. 24, a couple of weeks after eating a cantaloupe bought at a King Soopers grocery store. He has been in the hospital or a nursing home ever since. Mr. Stevens has filed a lawsuit against Jensen Farms, said his lawyer, William Marler.
Mr. Stevens’s daughter, Jeni A. Exley, said she worried that he would no longer be able to take care of himself once he finally was able to go home. “He’s surprised that he survived it, being that there’s so many deaths,” Ms. Exley said. “We should be able to trust the U.S. food supply, but I don’t think you can right now.”
What Is Listeria? Listeria monocytogenes leads a double life. It's commonly found in the environment, where it feeds on decaying plant matter. It's found in soil, animal feed, groundwater, and sewage. It can also be carried in the guts of cattle and poultry.
But when listeria gets into humans, it changes form. It becomes a bacterial parasite that lives inside -- and feeds on -- human cells. The disease caused by listeria is called listeriosis.
People with lowered immunity -- the elderly, cancer patients, people taking immunity-suppressing drugs, and pregnant women -- are particularly vulnerable to listeriosis.
All of the cantaloupes in the current listeria outbreak came from Jensen Farms, a Colorado-based company. Although some of these cantaloupes carry a distinctive sticker, not all contaminated fruit will be marked. Ask your grocer if the cantaloupe you bought is from Jensen Farms.
If you suspect that you have a contaminated cantaloupe, do not try to wash off the listeria. Griffin of the CDC notes that it's not clear whether a listeria-contaminated melon carries listeria on the inside as well as on the outside.
So dispose of suspect cantaloupe in a sealed bag, and make sure it will not be eaten by animals or other people.
But that's not all you should do.
One study found that once a listeria-contaminated food product was in a person's home, 11% of all food samples in their refrigerators also were contaminated. Nearly two-thirds of people with listeria infections turn out to have listeria growing in their refrigerators.
So clean your refrigerator if you think you may have purchased a contaminated cantaloupe. Wash the fridge thoroughly with soap and water. Then wipe it down with a diluted solution of chlorine bleach.
One Tough Bug HYG-5562-98 Nancy Stehulak
Listeria are bacteria found frequently in the environment. One listeria species, Listeria monocytogenes, can cause the serious foodborne illness "listeriosis." Listeriosis is a bacterial infection. Approximately 425 deaths occur each year in the United States due to L. monocytogenes.
L. monocytogenes is somewhat unusual in that it will grow at refrigeration temperatures. It is slightly more heat resistant than many other bacteria such as salmonella and E. coli, and will grow at temperatures as high as 140 to 150 degrees F. It will not survive pasteurization or heat treatment. Freezing seems to have little effect on the bacteria.
Where does L. monocytogenes come from? L. monocytogenes has been found in soil, leaf litter, sewage, silage, dust, and water. The organism often moves through animals and humans without causing illness, and has been found in many domestic and wild animals, including birds and fish.
It has only been in the last decade that L. monocytogenes has been recognized as an agent of foodborne illness.
Who is at risk? Healthy people rarely contract listeriosis, but the illness can be serious for some people, especially the elderly, newborns, pregnant women, and those with weakened immune systems.
Foods Associated with Listeriosis L. monocytogenes has been associated with such foods as raw milk, unpasteurized milk, cheeses (particularly soft-ripened varieties), ice cream, raw vegetables, raw-meat sausages, raw and cooked poultry, raw meats (all types), and raw and smoked fish. Its ability to grow at temperatures as low as 37 degrees F permits multiplication in refrigerated foods.
The Illness-What are the symptoms? Consumers most commonly contract listeriosis by eating food contaminated with the organism. Healthy people do not often develop noticeable listeriosis symptoms after eating food containing L. monocytogenes. The highest incidence of listeriosis has been in persons over 60 years old and newborns. Infections that occur during pregnancy may lead to miscarriages or serious illness in newborns. Others most at risk include those with compromised immune systems due to cancer, AIDS, or medications that impact the immune system.
Symptoms are fever, fatigue, nausea, vomiting, and diarrhea. More serious symptoms can result in meningitis (brain infections) and septicemia (bacteria in the bloodstream). Pregnant women may contract flu-like symptoms of listeriosis; complications can result in miscarriage, stillbirth, or meningitis in the newborn.
How can I reduce my risk? L. monocytogenes in food cannot be seen, tasted, or smelled. Common sense and simple precautions that apply to any foodborne illness should be used. Good sanitation, personal hygiene, and safe buying, storing, cooking, and serving methods, when applied in home, retail, and food service environments, can reduce the risk of problems with L. monocytogenes.
Although most of the population is at very low risk for listeriosis, the risk can be reduced if you:
1. Thoroughly cook all food of animal origin.
2. Wash raw vegetables thoroughly before eating.
3. Keep uncooked meats separate from vegetables, cooked foods, and ready-to-eat foods.
4. Avoid raw/unpasteurized milk or foods made from raw milk.
5. Wash hands, knives, and cutting boards after handling uncooked foods.
6. Read and follow label instructions to "keep refrigerated" and "use by" a certain date.
References 1. U.S. Department of Agriculture, Food Safety and Inspection Service, Background Document March 1992. Preventing Foodborne Listeriosis.
For more information on foodborne illness, contact your local county Extension Agent. See also the additional fact sheets on foodborne illness.
A Case in Point ... In 1985, an outbreak of Listeriosis, due to Mexican-style cheese, led to 18 deaths and numerous stillbirths. As a result of this episode, FDA has been monitoring domestic and imported cheeses and has taken numerous actions to remove these products from the market when L. monocytogenes is found.
The Center for Disease Control has established an epidemiological link between consumption of raw hot dogs or under cooked chicken in approximately 20% of the sporadic cases under study.
Source: U.S. Department of Agriculture, Food and Safety Inspection Service, Food and Drug Administration, Background Document, March, April 1992.
This material is based on work supported by the Extension Service, U.S. Department of Agriculture, under special project number 96-EFSF-0-3500.
How does Listeria monocytogenes get into food?
Animals can carry Listeria monocytogenes in their intestines without becoming sick. As a result, the bacteria may be spread to meat and dairy products. Listeria monocytogenes is killed by cooking or by other heating methods, such as pasteurization, used to produce ready-to-eat foods. However, ready-to-eat food can become contaminated after processing within the processing plant or along the route from the plant to your plate. Outbreaks of listeriosis are associated with ready-to-eat foods such as hot dogs, luncheon meats, cold cuts, fermented or dry sausage, and other deli-style meat and poultry. In the home, Listeria monocytogenes is destroyed if ready-to-eat foods are reheated to steaming hot
How does Listeria get into food? Listeria monocytogenes is found in soil and water. Vegetables can become contaminated from the soil or from manure used as fertilizer. Animals can carry the bacterium without appearing ill and can contaminate foods of animal origin such as meats and dairy products. The bacterium has been found in a variety of raw foods, such as uncooked meats and vegetables, as well as in processed foods that become contaminated after processing, such as soft cheeses and cold cuts at the deli counter. Unpasteurized (raw) milk or foods made from unpasteurized milk may contain the bacterium.
Listeria is killed by pasteurization and cooking; however, in certain ready-to-eat foods such as hot dogs and deli meats, contamination may occur after cooking but before packaging.
And the Food and Drug Administration is currently doing an investigation at the farm to figure out why, so we can prevent future cases of contamination. But the skin, the flesh of the cantaloupe is actually a good place for bacteria to grow. Listeria is quite unusual as a bacteria for a couple of reasons.
One is that, once you eat it, it may be one to three weeks or even one or two months before you become ill. And that's the main reason we expect to see, unfortunately, case numbers rising in the coming weeks. And the second is that it's one of those rare bacteria that can actually grow even when it's refrigerated.
So as you put it in your refrigerator, most food, even if it's contaminated, you will knock down that contamination. But with listeria, the bacteria can continue to grow in your refrigerator, and that's why we tell people to throw out anything from Jensen Farms, any cantaloupe from Jensen Farms.
What's tricky about listeria is that unlike most food-borne pathogens, it can multiply in the refrigerator. Pasteurization and cooking will kill the listeria bacterium, but contamination often occurs later in processing. So you might bring home some ready-to-eat deli meats, hot dogs or soft cheeses that have a trace of listeria contamination on them, put them in the fridge and a week or so later, while they still look fresh, find yourself eating a listeria-packed meal. Not that you would know right away. The symptoms of listeriosis can take anywhere from a few days to a few weeks to show up.
A nationwide listeria outbreak that as killed 25 people who ate tainted cantaloupe was probably caused by unsanitary conditions in the packing shed of the Colorado farm where the melons were grown, federal officials said Wednesday.
Government investigators said that workers had tramped through pools of water where listeria was likely to grow, tracking the deadly bacteria around the shed, which was operated by Jensen Farms, in Granada, Colo. The pathogen was found on a conveyor belt for carrying cantaloupes, a melon drying area and a floor drain, among other places.
“You’re rolling around cantaloupe on uncleanable equipment and you’re getting it wet and you’re not cooling it — it provides the perfect environment for listeria growth and spread,” said James Gorny, a senior food safety adviser at the Food and Drug Administration.
The outbreak, which began in late July, is the deadliest caused by foodborne disease since 1985. A total of 123 people in 26 states have fallen ill, including those who died, according to the Centers for Disease Control and Prevention.
Nicholas J. Parolisi Jr., a lawyer for Jensen Farms, said he could not comment on the F.D.A.’s accusations.
The farm had passed a food safety audit by an outside contractor just days before the outbreak began. Eric Jensen, a member of the family that runs the farm, said in an e-mail that the auditor had given the packing plant a score of 96 points out of 100.
F.D.A. officials did not criticize the auditor directly. But Michael R. Taylor, deputy commissioner for foods, said the agency intended to establish standards for how auditors should be trained and how audits should be conducted.
The food industry increasingly has come to rely on what it calls third-party audits of farms or processing plants to ensure the safety of food. But the auditors are hired by the companies being inspected, and their procedures are largely unregulated. In several recent food safety lapses, the facilities involved had passed third-party audits.
It was not clear how listeria initially got into the packing shed, which officials described as an open-air structure having a concrete floor, a roof and no walls.
Listeria is frequently found in soil or manure, but tests of the soil on the farm did not turn up the bacteria. Officials said that a dump truck used to take culled melons to a cattle farm was parked near the processing shed and could have brought bacteria to the facility.
Jensen Farms, run by Mr. Jensen and his brother Ryan, had recently acquired a set of used machinery to upgrade the way it washed and dried its cantaloupes. The equipment had been used to clean potatoes and was not intended for use with cantaloupes, officials said. They said the equipment was corroded in places and built in a way that made it difficult to clean and sanitize.
An area used to dry the melons included a cloth cover that could easily have harbored the bacteria, according to a person who discussed the operation with the Jensens.
Officials also said that the cantaloupes had not been adequately cooled before they were placed in refrigerated storage, which could have caused condensation to form on the fruit, creating hospitable conditions for listeria. The bacteria grow well in wet or damp conditions and can also thrive in cold.
Dr. Gorny said that some of the conditions he described, including pools of water on the floor, had been noted during a visit in mid-September after the plant ceased operation and the equipment was dismantled. It was not clear if investigators who had visited the plant while it was still in operation saw the same unsanitary conditions.
Officials said that conditions at Jensen Farms were not typical of the produce industry.
“We have no reason to believe these factors are indicative of practices throughout the industry,” said Sherri McGarry, a senior F.D.A. adviser.
The outbreak is likely to focus new attention on the use of auditors in the food industry. Typically farms or processors are required by their customers, like supermarket or restaurant chains, to have an auditor evaluate their food safety procedures.
Jensen Farms hired an auditor called PrimusLabs, based in California, to inspect its facility. Primus gave the job to a subcontractor, Bio Food Safety, which is based in Texas. Jensen and Primus declined to provide a copy of the audit report.
Robert Stovicek, the president of PrimusLabs, said his company had reviewed the audit and found no problems in how it was conducted or in the auditor’s conclusions.
“We thought he did a pretty good job,” Mr. Stovicek said. He said the auditor, James M. DiIorio, has been doing audits for the company since March.
He said that Mr. DiIorio had received two one-week training courses as part of his preparation and had also gone on audits with other auditors.
Asked how Mr. DiIorio could have given high marks to a facility that the F.D.A. described as a breeding ground for listeria, Mr. Stovicek said, “There’s lots of variations as to how people interpret unsanitary conditions.”
Mr. DiIorio did not return phone calls seeking comment.
Trevor V. Suslow, a professor of food safety at the University of California, Davis, said auditors may give farmers, processors and retailers a false sense of security. “There needs to be training, certification and auditing of the auditors,” he said.
Listeria can cause high fever and diarrhea, and cases can be especially severe among older people or those with weakened immune systems. Most of the people who died in the outbreak and many others who fell ill were elderly.
Herbert H. Stevens Jr., 84, of Littleton, Colo., became ill with a high fever on Aug. 24, a couple of weeks after eating a cantaloupe bought at a King Soopers grocery store. He has been in the hospital or a nursing home ever since. Mr. Stevens has filed a lawsuit against Jensen Farms, said his lawyer, William Marler.
Mr. Stevens’s daughter, Jeni A. Exley, said she worried that he would no longer be able to take care of himself once he finally was able to go home. “He’s surprised that he survived it, being that there’s so many deaths,” Ms. Exley said. “We should be able to trust the U.S. food supply, but I don’t think you can right now.”
What Is Listeria? Listeria monocytogenes leads a double life. It's commonly found in the environment, where it feeds on decaying plant matter. It's found in soil, animal feed, groundwater, and sewage. It can also be carried in the guts of cattle and poultry.
But when listeria gets into humans, it changes form. It becomes a bacterial parasite that lives inside -- and feeds on -- human cells. The disease caused by listeria is called listeriosis.
People with lowered immunity -- the elderly, cancer patients, people taking immunity-suppressing drugs, and pregnant women -- are particularly vulnerable to listeriosis.
All of the cantaloupes in the current listeria outbreak came from Jensen Farms, a Colorado-based company. Although some of these cantaloupes carry a distinctive sticker, not all contaminated fruit will be marked. Ask your grocer if the cantaloupe you bought is from Jensen Farms.
If you suspect that you have a contaminated cantaloupe, do not try to wash off the listeria. Griffin of the CDC notes that it's not clear whether a listeria-contaminated melon carries listeria on the inside as well as on the outside.
So dispose of suspect cantaloupe in a sealed bag, and make sure it will not be eaten by animals or other people.
But that's not all you should do.
One study found that once a listeria-contaminated food product was in a person's home, 11% of all food samples in their refrigerators also were contaminated. Nearly two-thirds of people with listeria infections turn out to have listeria growing in their refrigerators.
So clean your refrigerator if you think you may have purchased a contaminated cantaloupe. Wash the fridge thoroughly with soap and water. Then wipe it down with a diluted solution of chlorine bleach.